Monday, September 16, 2013

Readers Write In: Are Endangered Insects Burying Rats in my Yard?

Good afternoon!

I appear to have a mating pair of an endangered beetle that has not populated the state of Florida, or any bordering states, for a while.  

Unfortunately, I do not have pictures of the beetles themselves, as I only saw them momentarily.  I have, however, attached still images of the “proof” I have to my little neighbors’ identity.  Here is my story.

Yesterday afternoon (around 3:30), I stopped by my house and greeting us on our front porch was the carcass of a rat, courtesy of one of my outdoor cats (I have two).  I snapped a picture of it, made a few jokes with both kids about it becoming a zombie rat, we laughed, and I returned to work.

When I got home in the evening (about 7:00), the rat was off of the porch, about 10-11 inches further from where it had been laid out on the porch earlier in the afternoon.  Thinking my oldest may have done a “typical boy thing” and kicked it or something when he had gotten home, I asked if he’d moved it.  He said no, and was surprised that it was no longer on the porch.  More jokes about zombie rat ensued, but I figured it was one of the cats that moved it (for some unknown feline reason).

Upon further inspection (because now I was curious), I noticed what looked like the rat’s head (it was face-down at this point) pulsating up and down, followed by dirt shifting around its head.  I snapped another picture of it, suspecting it was being pulled into the earth by some burrowing creature.  Even through the smell, I watched, to confirm my suspicion.  It was during this time that I caught a couple glimpses of an orange and black insect, that would show up for very brief instances around the side of the rat’s head, in the dirt.

I snapped another picture of the carcass, with the intention of sharing my story on Facebook (which I have).  The dirt at this time was up to the rat’s ear. Closer inspection of this image shows orange spot in dirt near top of rat’s head; I caught a brief glance of one of the beetles!  There also appears to be a black and orange shape near the base of the rat’s tail; could this possibly be the mate?

The next morning I checked on the progress.  The rat was buried almost entirely, with only a foot, it’s very hind quarters, and its tail still exposed.  

I decided I needed to do a little research and find out who my friends were, that were saving me from cleaning up this smelly rat carcass.  My research yielded link after link to the American Burying Beetle, which is not thought to be in my region, let alone my state, anymore.  Excitement!  Not only did I have an endangered insect who cleaned up after my cats, but I have a mating pair!

If you know of anyone that could confirm my pair, that would be great.

Angela N.
Jacksonville, Florida

    This isn't the first time I've been asked to solve a mystery about mysteriously disappearing corpses in yards. As I wrote in that previous post, there are a number of invertebrates that carry out their life cycles by finding corpses of small animals, burying them, and/or consuming them and laying their eggs on it. It's quite a useful service, just think of all the rat bodies that we don't have to see (or smell) because of these little insects.

    These insects are beetles within the Silphidae family, which includes Carrion and Burying Beetles, like the American Carrion Beetle (Necrophila americana, is that a cool scientific name or what?). Beetles in the Necrophila genus (what I call the Carrion Beetles) tend to be large, robust insects with a black body and bright yellow head. They don't fit the description Angela provides. But, also within the Silphidae family is the Nicrophorus genus (what I call the Burying Beetles). These beetles have a black body and variously patterned orange spots. Now I think we have identified the culprit.

   But, there are a number of different Burying Beetles within the Nicrophorus genus and there's the rub. The most famous of these beetles is Nicrophorus americanus, the American Burying Beetle. This species is now very rare and we do not really know why. One theory is that they evolved to feed on the carcasses of Passenger Pigeons, a now extinct but once extremely plentiful source of dead bodies to eat. In any case, I am going to rule out the American Burying Beetle because A) it is extremely rare and B) it is never known to have occurred in Florida even when it was abundant long ago.

    My guess is that Angela observed the closely related Nearctic Burying Beetle (Nicrophorus orbicollis). With its orange spots and black body, this species closely resembles the much rarer American Burying Beetle. However, one key difference is that the shield behind the American Burying Beetle is orange, while it is black in the Nearctic Burying Beetle. In any case, I based my identification on the fact that Nearctic Burying Beetle is one of the most common species within its family and it is known from Florida.

    Burying beetles are fascinating. Male beetles will find a recent corpse and attract a female with pheromones. Once she arrives, they will mate and bury the corpse together. Afterwards, the female will lay eggs nearby so her grubs will have something convenient to eat after they hatch. Interestingly, the adults will hang around to protect and feed their young.

    Fascinating to see the photos of two burying beetles at work.

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